1. Field of Invention
The present invention relates to a fan system, in particular to a fan system and a power reverse protection apparatus thereof that can prevent the reverse transmission of the power signal.
2. Related Art
As the high development of technology, the demand to the function of the electronic device is higher, the number and the density of the electronic elements increase, and hence relatively larger amount of the electricity is used. When the amount of the electricity is large, a protective circuit is usually disposed at the input of the electronic device for protection. The efficiency of the protective circuit has a direct effect on the reliability and the lifetime of the electronic device.
A power reverse protection apparatus disposed at the input of the electronic device is usually used to turn on the main power circuit in the electronic device and to turn off the rest of the power circuits. However, the amount of electricity is also consumed while driving the power reverse protection apparatus. Therefore it is an important subject to reduce the power consumption of the power reverse protection apparatus.
Referring to FIG. 1, as disclosed in U.S. Pat. No. 6,611,410, the conventional power reverse protection apparatus 10 includes an N-type metal oxide semiconductor field effect transistor (N-type MOSFET) 102, which includes a body diode transistor BD1, a plurality of coils (can be regarded as inductors) L1 to LN, a plurality of diodes D1 to DN, a plurality of switches S1 to SN, a capacitor 16, and a capacitor 108. Since the inductor is an energy storage element, as the voltage supply VSUPPLY provides a surge voltage that passes through the body diode BD1, a current is generated and flows to the coils (the inductors) L1 to LN. As the current increases, the coils L1 to LN impede the current increase and temporally store the electric energy in the form of magnetic field, and a high voltage at the two ends of the capacitor 16 thus will be generated. This high voltage will turn on and drive the N-type MOSFET 102 and activate the power reverse protection apparatus 10. If the power reverses instantly, which means, when the voltage supply VSUPPLY is a low potential or a negative potential, the body diode BD1 can be used as a power reverse protection diode and the N-type MOSFET 102 is turned off. However, if a plurality of coils L1 to LN are used to store the energy to drive the N-type MOSFET 102, the coils will take a lot of space and the cost of the coil material is high. The circuit will be more complex and it is harder to control. In addition, driving the capacitor 16 by a high voltage consumes too much power.